This invention relates to methods and systems for radio communications, and more particularly to methods and systems for wirelessly broadcasting messages to wireless terminals such as radiotelephones.
Commercial radio communications are widely used for voice and/or data communications. Pagers and cellular phones, in particular, have become relatively common. These two different types of communication devices, and supporting systems, have evolved from different fundamental purposes. In particular, pagers traditionally provide one-way, limited information to one or more end users and cellular phones traditionally provide two-way voice communication service.
As time and technology progress, the traditional functional dividing lines between these two different types of radio communication devices have become blurred. Pagers have acquired some of the functionality that was traditionally provided by cellular phones and vice-versa. For example, two-way pagers have been developed which permit the pager user to transmit messages to the paging system, which messages can then be forwarded to other parties. Similarly, cellular phones have acquired the capability to transmit and receive short (e.g., on the order of 160 alphanumeric character) text messages which can be output on the display of a cellular phone.
This evolution in radio communication devices has led to the development and marketing of a host of new information services. For example, paging systems have been implemented which provide for the broadcast of information services, e.g., stock quote information services, to a large number of subscribers that have pagers with displays. These pagers periodically receive information over an air interface associated with a large number of stocks or other financial instruments such as options, futures. etc., and display the current prices of these instruments so that a user can track a portfolio""s performance.
Users of cellular phones may have interest in the provision of a similar service which would provide information service support in a cellular network. However, cellular systems, unlike paging systems, have conventionally been designed around the paradigms of (1) limited bandwidth due to a restriction on the spectrum allocated by various governing bodies such as the FCC for cellular applications and (2) the notion that most of the limited bandwidth should be reserved for point-to-point connections such as voice connection between the cellular phones and the system, with only a relatively small fraction being reserved for broadcast (point-to-multipoint) transmissions from the system to the cellular phones operating in the system. Due to this latter feature of cellular systems in particular, system designers generally are very careful regarding the amount of information transmitted on the available broadcast channels and the frequency with which this information is repeated. Thus, the provision of broadcast information services to cellular radio communication systems may not readily be accomplished by the most straightforward approach of broadcasting whatever information is desired for all subscribers to display on their cellular phones.
For example, in a Time Division Multiple Access (TDMA) cellular radiotelephone system, each radio frequency is divided into a series of time slots, each of which contains a burst of information from a data source, e.g., a digitally encoded portion of a voice conversation. By time multiplexing bursts associated with different sources, more than one channel can be supported on each radio frequency. The time slots are grouped into successive TDMA frames having a predetermined duration. The number of time slots in each TDMA frame is related to the number of different users that can simultaneously share the radio channel. If each slot in a T DMA frame is assigned to a different user, the duration of a TDMA frame is the minimum amount of time between successive time slots assigned to the same user.
The successive time slots assigned to the same user, which are usually not consecutive time slots on the radio carrier, constitute the user""s Digital Traffic Channel (DTC). As mentioned above, this is typically a point-to-point resource. In fact, TDMA systems generally reserve the majority of the available radio channels for use as DTCs to ensure a large traffic capacity. However, as described in more detail below, Digital Control CHannels (DCCHs) are also provided for communicating control signals and overhead information, including a mechanism for connecting to the radio communication system and being assigned a DTC.
Similar types of resource allocations are found in other types of cellular systems. For example, in Code Division Multiple Access (CDMA) systems, channelization is performed by spreading data associated with a particular connection using a unique spreading code. This code, as opposed to or in conjunction with frequency and time differentiators, provides the receiver with a mechanism for extracting its intended data, by correlating the received composite signal with the code assigned to its traffic channel. Like TDMA systems, CDMA systems can also provide for broadcast control channels or other overhead signaling channels by allocating known codes thereto. However, like TDMA systems, CDMA systems also tend to reserve more resources, such as codes and power, for dedicated traffic channels than for broadcast information channels. Accordingly, it would be desirable to provide methods and systems which are able to provide broadcast information services within the constraints of existing cellular radio communication systems. In particular, it would be desirable to design broadcast information methods and systems that can accommodate an end user""s desire for a relatively large quantity of data that may need to be updated relatively frequently, while reducing and preferably minimizing the usage of scarce broadcast channel resources.
GSM systems presently can offer broadcast services. ANSI 136 has defined a broadcast channel that provides enhanced flexibility with respect to bandwidth allocation, sub-channelization, content description and change notification. However, broadcast services may not be extensively used in the future for the ANSI 136 or ANSI 95 technologies.
Packet data communication, a point-to-point form of communication, may provide access to the same services. Packet data communication, using for example GPRS as will be the supported in both GSM and ANSI 136, are being elaborated in the standards setting groups and resources are being assigned to the development of such products by vendors. Thus, the user may use a packet data service to access an Internet-based stock quote service in which the user""s portfolio is downloaded to a wireless terminal upon request by the user. Using a broadcast service, all the securities, possibly limited to a subset of all available securities in interest of bandwidth limitation, are sent on a broadcast channel. The wireless terminal continually or as a result of a user request reads the entire set of securities on the broadcast channel and further manipulation of the data. For example, extraction of the data for presentation as defined by the specific user""s portfolio may take place in the mobile station or in a companion lap-top computer.
Wireless packet data systems are now being developed and being made available. This is amplified by the ITU initiated development of xe2x80x9c3:e generationxe2x80x9d wireless systems. A focus of this activity is to provide a packet data services as efficiently as possible with bit-rates of 144 kbit/s, 384 kbit/s and 2 Mbit/s depending on the environment. To provide wireless packet data, the operators may only need to obtain the necessary equipment and then the user can access the Internet or a corporate mail system. However, the operator may then only provide a wireless bit-pipe but no content. The content provider may be the same companies that provides content in the wireline environment. A current trend in the Internet is for these companies to try to establish themselves as Internet xe2x80x9cportalsxe2x80x9d for as many users as possible. The portals, or entry points to the world wide web, generate revenue by providing advertisements on their sites.
It may be difficult for wireless operators to extend beyond providing connectivity to the existing and ever increasing Internet-based content provider. There are several reasons for the possible inability of the wireless operators to provide connectivity but not provide very much content. The development of broadcast services may require the operators to assign resources for the definition and specification of the services. For the example of the stock quote service, an additional step of translating the format and content from the data source into the format of the broadcast channel may be necessary. Charging mechanisms and associated content access control may need to be developed in order to generate revenue for the operators. A method for access control of broadcast services is disclosed in application Ser. No. 09/132,232, to the present inventor, filed Aug. 11, 1998, and assigned to the assignee of the present application, the disclosure of which is hereby incorporated herein by reference in its entirety.
However, providing a broadcast channel with stock quotes, sport results, weather reports etc. could provide an increased revenue stream for the wireless operator. Furthermore, a broadcast channel need not use up-link communication. The required bandwidth can be independent of the number of users and user request of the information whereas for the packet data scenario the bandwidth used generally is proportional to these two variables. Thus, for services that are widely subscribed to, a broadcast service may be more spectrum efficient then having all users make individual accesses to get information such as their stock portfolios.
If there are very few users subscribing to a service a packet data solution may be more efficient. Applications can be built which use a combination of broadcast and point-to-point service that can allow better control of bandwidth usage than only using one of the type of channels. For example, application Ser. No. 09/114,350, to the present inventor, filed Jul. 13, 1998, and assigned to the assignee of the present application, discloses a xe2x80x9cheadline newsxe2x80x9d service which is broadcast and the content is hyperlinked to more detailed information located in a service server. When the user selects an item or topic, the mobile station generates a point-to-point communication to the service server which may be a world wide web site or the detailed content may be downloaded to the mobile station. Thus, broadcast services may allow the operators to receive revenue for value added services and may be more efficiently, provided than packet data services.
It is therefore an object of the present invention to provide improved methods and systems for wirelessly broadcasting messages to wireless terminals.
It is another object of the present invention to provide systems and methods for wirelessly broadcasting messages to a plurality of radiotelephones in a cellular system.
It is still another object of the present invention to provide systems and methods that can allow relatively long messages to be broadcast over wireless communication systems having relatively short message service capability.
These and other objects are provided, according to the present invention, by systems and methods that wirelessly broadcast a message to a plurality of wireless terminals by error correction coding the message to produce an error correction coded message block, dividing the error correction coded message block into a plurality of frames and error correction coding the frames to produce a plurality of error correction coded frames. The plurality of error correction coding frames are wirelessly broadcast to the plurality of wireless terminals. At the wireless terminals, the plurality of frames are received and the frames are error correction decoded to produce a plurality of error correction decoded frames. The plurality of error correction decoded frames are combined into a message block, and the message block is error correction decoded to produce the message.
It has been found, according to the present invention, that by error correction coding the entire message in addition to error correction coding the frames of the message, long messages may be reliably broadcast and received, notwithstanding fading and other problems in the transmission. Accordingly, a broadcast channel that is designed for short message usage also may be used to reliably transmit long messages.
In a preferred embodiment of the present invention, the frames are also error detection coded in addition to error correction coded. Preferably, the message is error correction coded using block coding, and the frames are convolutionally coded.
In order to provide systems and methods that are compatible with existing short message service systems and methods, an indication is provided that the error correction coded message block is error corrected. The indication may be provided within the error correction coded message block, or outside the error correction coded message block. Preferably, an indication of at least one of the type of error correction coding and the amount of error correction coding in the error coded message block is provided. Moreover, the message is preferably wirelessly broadcast for multiple cycles, and an indication is also preferably provided of the number of cycles of retransmission and an identification of the current cycle number.
The invention may, for example, be applicable to a TDMA system that includes a Digital Control CHannel (DCCH) having a short message Service Broadcast Control CHannel (S-BCCH) logical channel. The message is error correction coded to produce an error correction coded message block and the error correction coded message block is divided into a plurality of frames. The frames are error correction coded to produce a plurality of error correction coded frames. The plurality of error correction coded frames are then placed in the S-BCCH logical channel. The S-BCCH logical channel is then wirelessly broadcast to the plurality of radiotelephones in a plurality of TDMA time slots.
At the TDMA wireless terminals, the plurality of TDMA frames including the DCCH are wirelessly received. At least a portion of the S-BCCH in the DCCH is error correction decoded to produce a plurality of error correction decoded frames. The plurality of error correction decoded frames are combined into a message block, and the message block is error correction decoded to produce the message.
As described above, an indication is preferably provided that the message is error correction coded. The indication may be provided within the S-BCCH or outside the S-BCCH. Preferably, the DCCH includes a Message Type (MT) field and the indication is provided implicitly in the MT field. Alternatively, the indication may be provided explicitly in another field. In another alternative, the message includes a Fast-BCCH (F-BCCH) and an Extended-BCCH (E-BCCH). The indication is provided in the F-BCCH or the E-BCCH, that at least one message in the S-BCCH is error correction coded.
In a TDMA system, the error correction coding of the message is preferably performed by block coding, and the error correction coding of the frames is preferably provided by convolutional coding. The frames may be convolutionally coded at less than rate {fraction (1/2)} convolutional coding, due to the added coding that is provided in the message block. At the TDMA wireless terminal, error correction decoding at least a portion of the S-BCCH in the DCCH is performed in response to receiving an indication that at least a portion of the S-BCCH is error correction coded. As described above, the indication may be provided within or outside the S-BCCH. Accordingly, robust broadcast of relatively long messages may be provided in wireless communications systems having relatively short message service capability.